Plasma chambers commonly are used to perform processes for fabricating electronic devices such as semiconductors, displays and solar cells. Such plasma fabrication processes include chemical vapor deposition of semiconductor, conductor or dielectric layers on the surface of a workpiece or etching of selected portions of such layers on the workpiece surface.
It is important for a plasma fabrication process to be performed with high spatial uniformity over the surface of the workpiece. That is, a deposition process should be performed so that the deposited material has uniform thickness and quality at all positions on the surface of the workpiece. Likewise, an etch process should etch material at a uniform rate at all such positions. Spatial uniformity of a plasma fabrication process typically requires spatial uniformity of the density of the plasma adjacent the surface of the workpiece.
One approach for increasing the manufacturing throughput of a plasma chamber is to process two or more workpieces within the plasma chamber simultaneously. However, processing multiple workpieces within the plasma chamber increases the difficulty of achieving spatial uniformity of the density of the plasma adjacent the surface of the workpiece.